Howard Collins, London Undergrounds chief operating officer, said: "The Queen thought it was marvellous. She said, 'What a fantastic gift.’ There was a big smile on her face.

"She was saying about how busy [the Underground] is. She travelled on the Tube as a young lady. She recognised it was very busy."

The Queen first travelled on the Tube in May 1939, when she was 13 years old and still a Princess. She was pictured with her governess Marion Crawford and Princess Margaret.

Ironically, she might have been better off travelling by Tube yesterday, as her car broke down during the City tour, and she had to cadge a lift with the police. The Telegraph have more on this.

Perhaps she may be more used to London Underground travel than she lets on. Crash Calloway said: "I am led to understand that she has her own private underground stop anyway, doesn't she? Some kind of secret Tube stop/tunnel in case of Nuclear War or Revolution... " Stranger things have happened.